During certain processing of interlaced video signals, and particularly those that have been digitized, there is apparent visual evidence of temporal shift upon a display of an image created by those video signals. Portions of certain types of images, for example, visually appear to be moving backward, with this effect being particularly observed when the images are magnified. When the interlaced video image is enlarged, an odd (or even) number of line shifts may occur in the picture elements (pixels). Even though conventional interlaced images refresh their display every field, for example, at sixty times a second, the temporal reversal of output relative to input may be perceptible to a viewer.
One such area in which this temporal (and spatial) shift become apparent is in the systems described in commonly-owned U.S. Pat. Nos. 5,185,667 issued Feb. 9, 1993, 5,313,306 issued May 17, 1994 and 5,359,363 issued Oct. 25, 1994. The contents of these patents are incorporated herein by reference as to their entire contents.
In the technology described in these patents, video signals are electronically processed for their transformation according to pan and tilt orientation, rotation and magnification so as to view any selected portion of a total video image under selected conditions. Such transformation is generally referred to in the art as "affine transformation." The affine transformation causes single line shifts in the vertical position of pixels which, in an interlaced image, result in a temporal reversal of the display of the transformed dynamic image. Such reversal is disconcerting to some users of the technology of the cited patents.
in order to minimize these effects, these patents teach using magnification on specific fixed increments. In one, wherein the magnification (really minification) is 1/2.times., every other line is discarded which results in a reduction of input image frequency, called fields, from sixty fields per second to thirty fields per second. This removes the time reversal, but at the same time leads to a reduction in the apparent update rate of moving objects in the input image.
Also, it is common to use a 2.times. magnification, that is, doubling the magnification by doubling the input lines vertically and the number of pixels horizontally. This, however, does not provide an improvement in the reversal problem, and further provides images of objects that appear to have "fingers" or extensions that do not 0have the proper time relationship.
In addition, it is conventional to utilize filters for deinterlacing. However, this has not been applied to the capture, transformation, magnification, rotation and reconstitution of interlaced images for both input and output.
Accordingly, it is an object of the present invention to provide a method for eliminating the temporal shifts that occur during affine transformation of interlaced video images.
Another object of the present invention is to provide apparatus to carry out the present method for eliminating the temporal shifts.
A further object of the present invention is to provide a method for eliminating distortion caused by temporal shifts that occur during transformation of interlaced video images for the purpose of selecting pan and tilt orientation, rotation and magnification of at least a selected portion of the interlaced video images.
It is also an object of the present invention to provide modified apparatus for transforming interlaced video images according to pan and tilt orientation, rotation and/or magnification whereby temporal and spacial shifts that occur during such transformation are eliminated thereby making an output image more satisfactory to a viewer of these output images.
These and other objects of the present invention will become apparent upon a consideration of the drawings set forth below, together with a complete description thereof.